A typical steam turbine plant may be equipped with a high pressure steam turbine, an intermediate pressure steam turbine and a low pressure steam turbine. Each steam turbine is formed of materials appropriate to withstand operating conditions (pressure, temperature, flow rate, etc.) for that particular turbine.
Recently, steam turbine plant designs directed toward a larger capacity and a higher efficiency have been designed that include steam turbines that operate over a range of pressures and temperatures. The designs have included high-low pressure integrated, high-intermediate-low pressure integrated, and intermediate-low pressure integrated steam turbine rotors integrated into one piece and using the same metal material for each steam turbine. Often, a metal is used that is capable of performing in the highest of operating conditions for that turbine, thereby increasing the overall cost of the turbine.
A steam turbine conventionally includes a rotor and a casing jacket. The rotor includes a rotatably mounted turbine shaft that includes blades. When heated and pressurized steam flows through the flow space between the casing jacket and the rotor, the turbine shaft is set in rotation as energy is transferred from the steam to the rotor. The rotor, and in particular the rotor shaft, often forms of the bulk of the metal of the turbine. Thus, the metal that forms the rotor significantly contributes to the cost of the turbine. If the rotor is formed of a high cost, high temperature metal, the cost is even further increased.
Accordingly, it would be desirable to provide a steam turbine rotor formed of the least amount of high temperature materials.